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The endothelo-protective activity of a series of low-molecular oxygen-derived free radical scavengers (OFRS) was tested in rats. A model of endothelaemia provoked by intravenous administration of hydrogen peroxide was used. With each OFRS the activity in the hydrogen peroxide model was compared with that in the less specific model using the provocation by citrate as a calcium chelating agent. Relatively unspecific but biologically important OFRS, ascorbic acid, tocopherol, troxerutin and glutathione were tested in the first phase of the study. A marked optimum of endothelo-protective activity was shown with all agents, the optimum against hydrogen peroxide having been observed at doses from 3 to 50 times lower than against citrate. Ascorbic acid, troxerutin and the combination of both were also tested in another model based on leg ischaemia produced by ligature of the common femoral artery. Without OFRS, a marked increase of endothelaemia was observed after 30-60 min ischaemia showing a second peak after the release of the ligature. This second peak was completely abolished by the preventive administration of OFRS in a dose which was also effective in the hydrogen peroxide model.

A new method of endothelaemia estimation was used to investigate the production of vessel wall lesions by various drugs in rats. Increased endothelaemia was observed after endotoxin, activation of the blood contract system, hyaluronidase, streptokinase, anoxia and vasoactive drugs.

A quantitative model of stasis-type of venous thrombosis in rats is described. The ligated bowel loop was used after provocation by an injection of kaolin. The mesenteric vessels of the loop were cut in a dish filled with distilled water and the extinction of escaped haemoglobin was measured photometrically. Heparin was highly effective in this model. Vessel wall lesion may be used or inducing thrombosis instead of kaolin.